As an applying field of energy storage technique is enlarged to a cellular phone, a camcorder, a laptop PC and an electrical vehicle, efforts on studying and developing batteries have been increasingly embodied.
In consideration of this aspect, an electrochemical device receives the most attention. Particularly, according to the trend of electric devices having small size and light weight, efforts on developing a lithium secondary battery having small size, light weight and capable of charging and discharging in high capacity have been continued.
The lithium secondary battery is composed of a cathode and an anode, which include an electrode active material that may intercalate and deintercalate lithium ions, a separator disposed therebetween and an electrolyte as a delivering medium of the lithium ions.
As the electrolyte, an electrolyte of a liquid state, particularly, an ion conductive organic liquid electrolyte obtained by dissolving a salt in a non-aqueous organic solvent has been widely used. However, with the liquid electrolyte, leakage may be generated, and ignition and explosion may be induced due to the high flammability of the non-aqueous organic solvent used. In addition, with the liquid electrolyte, a carbonate organic solvent may be decomposed during charging and discharging a lithium secondary battery, or a side reaction with an electrode may be carried out to generate a gas in a battery. The side reaction may be further accelerated during storing at a high temperature to increase the amount of the gas generated. The gas consistently generated may induce the increase of the inner pressure of the battery, leading the modification of the battery including the expansion of the thickness of the battery. In addition, the local difference of adhesiveness may be generated on the surface of the electrode of the battery, and electrode reaction may not be carried out uniformly on the entire surface of the electrode.
Recently, a method of using a gel polymer electrolyte causing no concern of leakage, etc. has been suggested to overcome the safety problem of an electrolyte having a liquid state. The gel polymer electrolyte is manufactured by impregnating a polymer matrix formed by the polymerization reaction of a polymerizable monomer and a polymer initiator with an electrolyte including an electrolyte salt and a non-aqueous organic solvent and then, gelling.
However, since the gel polymer electrolyte also includes the non-aqueous organic solvent, defects concerning thermal safety still are mentioned. In addition, since inferior battery performance is attainable when compared to a battery using a liquid electrolyte, there are limits on commercialization.